1. Field of the Invention
The present invention relates to an image recording method and apparatus using a multi-beam, in which an image is recorded by moving a plurality of light beams relatively to a sub-scan direction of a photosensitive material and simultaneously carrying out main scan of a plurality of light beams, namely, an image recording method and apparatus in which an image is recorded on a photosensitive material by carrying out main scan of a plurality of light beams while the photosensitive material is being moved in a sub-scan direction.
2. Description of the Related Art
There has conventionally been known, as a method of recording an image on a photosensitive planographic printing plate such as a PS plate, a method in which a photographic film for plate-making (process film) on which the image is recorded is superposed on the photosensitive planographic printing plate.
The photographic film for plate-making on which the image is recorded is generated by image recording processing of an image recording apparatus referred to as a film setter, and development processing of a developing apparatus.
A magazine in which an elongated photographic film for plate-making wound in a layered form is accommodated is set in the film setter.
An exposure drum is rotated at a predetermined speed so as to move the photographic film for plate-making in a sub-scan direction. An image recording apparatus is disposed in a radial direction of the peripheral surface of the exposure drum on which the photographic film for plate-making is closely held.
The image recording apparatus distributes (swings) a plurality of light beams emitted from a laser in an axial direction of the exposure drum by a plurality of optical systems (main scan by a multi-beam system). As a result, main scan is carried out with the plurality of light beams while the photographic film for plate-making is being subjected to sub-scan, and the main scan is carried out repeatedly. The light beams are subjected to on-off control (or duty control) based on image information, and therefore, a predetermined image is recorded on the photographic film for plate-making.
The photographic film for plate-making on which an image is recorded is guided to an ordinary conveying path and discharged from the film setter, and further conveyed to a developing apparatus in a subsequent process.
When a print obtained from a photosensitive planographic printing plate is a color image, it is necessary that photosensitive planographic printing plates be provided respectively for four color components of cyan (C), magenta (M), yellow (Y), and black (K), that is, four sheets of photosensitive planographic printing plate, be prepared for each image.
Respective relative positions of images recorded on four photosensitive planographic printing plates are provided to coincide with one another, and a print of a full-color image can be obtained with four images overlapping with one another.
During recording of images, sub-scan movement of the photographic film for plate-making constantly continues, and therefore, recording of an image is started from a starting position of image recording (an initial position in a region to which light beam is applied in main scan), which comes first after a leading end of the photographic film for plate-making, that is, a position of a line at which main scan can be started, has been detected by the image recording apparatus. At this time, there is no correlation between the sub-scan movement of the photographic film for plate-making and the main scan of light beam.
Accordingly, respective images of the component colors are recorded in a state of being displaced from one another by an amount of about one sub-scan at the maximum. The amount of one sub-scan becomes larger in the widthwise dimension as a beam number of a multi-beam (the number of light beams) increases. For example, when exposure is carried out for 96 lines/mm using 6 light beams, a beam pitch is about 10 xcexcm, and therefore, the maximum amount of displacement becomes 60 xcexcm. An allowable amount of displacement in a print is limited to 100 xcexcm at its maximum, and if an amount of displacement at a starting position of writing amounts to 60% or more of the allowable amount of displacement, the displacement caused by other factors such as a conveying system, a positioning punch hole, and the like is hardly allowed. As a result, color displacement occurs to thereby deteriorate image quality.
In view of the above-described circumstances, an object of the present invention is to provide an image recording method and apparatus in which an amount of displacement of relative positions of images on a plurality of photosensitive materials can be limited to a pitch of one line irrespective of the beam number of a multi-beam and deterioration of image quality caused by color displacement or the like can be prevented.
A first aspect of the present invention is an image recording method, comprising the steps of: (a) providing at least two sets of image data separated by color, for an image; (b) recording a separated image corresponding to each set of image data on a section of photosensitive material moving in a sub-scan direction while the photosensitive material is being subjected to main scanning by a plurality of light beams; and (c) providing for relative positions of separated images on the section of photosensitive materials to substantially coincide with each other by setting a blank raster line in a first main scan for each section of the photosensitive material.
A second aspect of the present invention is an image recording method according to the first aspect, wherein in the step of providing for relative positions of the images, the number of blank raster lines in the first main scan is set for each section of the photosensitive material, based on a distance between a predetermined reference position on each section of the photosensitive material and a position at which the first main scan is started on that section.
A third aspect of the present invention is an image recording method according to the second aspect, wherein as the distance between the predetermined reference position and the position at which the first main scan is started becomes smaller, the number of blank raster lines is set larger.
A fourth aspect of the present invention is an image recording method according to the second aspect, wherein the upper limit of the number of blank raster lines is equal to the number of light beams in the plurality of light beams, minus one light beam.
A fifth aspect of the present invention is an image recording method according to the first aspect, wherein the blank raster lines are set in order from a leading end of the sheet of photosensitive material, the blank lines being substantially transverse to a direction in which the sheet of photosensitive material is conveyed.
A sixth aspect of the present invention is an image recording apparatus for recording an image on photosensitive material, wherein the image is represented by at least two sets of image data separated by color, the apparatus comprising:(a) image recording means for recording a separated image corresponding to each set of image data on a section of photosensitive material, by carrying out main scans of the photosensitive material with a plurality of light beams; (b) photosensitive material detecting means for detecting that a section of photosensitive material has been conveyed to a position at which an image can be recorded thereon; (c) state detecting means for detecting a state in which a main scan by the plurality of light beams can be started; (d) controlling means for controlling starting a main scan by the plurality of light beams, when the controlling means being in communication with the state detecting means receiving a signal therefrom that a main scan can be started and the photosensitive material detecting means has detected that a section of photosensitive material has been conveyed to a position at which an image can be recorded thereon; (e) calculation means for calculating an amount of distance by which a section of photosensitive material is conveyed, between a time when the photosensitive material detecting means detects that a section of photosensitive material has been conveyed to a position at which an image can be recorded thereon, and a time when the state detecting means detects a state in which a main scan by the plurality of light beams can be started; and (f) setting means for setting a number of blank raster lines in a first scan for each section of photosensitive material.
A seventh aspect of the present invention is an image recording apparatus according to the sixth aspect, wherein the number of blank raster lines in the first main scan is set based on the amount of distance by which the section of photosensitive material is conveyed.
An eighth aspect of the present invention is an image recording apparatus according to the sixth aspect, wherein as the amount of distance by which the photosensitive material is conveyed becomes smaller, the number of blank raster lines set by the setting means increases.
A ninth aspect of the present invention is an image recording apparatus according to the sixth aspect, wherein the upper limit of the number of blank raster lines is smaller than the number of the plurality of light beams by one.
A tenth aspect of the present invention is an image recording apparatus according to the sixth aspect, wherein the section of photosensitive material includes a leading end and the blank raster lines are set in order from the leading end of the section of photosensitive material in a direction in which the photosensitive material is conveyed.
An eleventh aspect of the present invention is an image recording apparatus for recording an image on a photosensitive material, wherein the image is represented by at least two sets of image data separated by color, the apparatus comprising: (a) a conveyor for conveying photosensitive material along a conveying path; (b) an image recording section having a scanner, in which a plurality of light beams is directed from the scanner across the conveying path for scanning an image onto photosensitive material being conveyed therealong, the image recording section providing a signal indicative of when scanning by the resonant scanner can begin; (c) a sensor which provides a signal indicative of a position of the photosensitive material along the conveying path; and (d) a controller receiving the image data and being in communication with the image recording section and the sensor, the controller receiving the signals from the image recording section and the sensor, and controlling the image recording section to record an image for each set of image date on different sections of the photosensitive material, the controller determining an amount a section of photosensitive material has been conveyed along the conveying path based on when the controller received a signal from the sensor and a signal from the image recording section, wherein the controller controls the image scanning section to set a number of blank raster lines in a first scan of each section of photosensitive material, based on the amount that the respective section of photosensitive material has been conveyed.
A twelfth aspect of the present invention is an image recording apparatus according to the eleventh aspect, wherein the scanner is a resonant type scanner.
A thirteenth aspect of the present invention is an image recording apparatus according to the eleventh aspect, wherein the number of blank raster lines decreases as the amount that the respective section of photosensitive material has been conveyed, increases.
A fourteenth aspect of the present invention is an image recording method in which an image is separated into plural image data based on plural colors, and based on the image data, an image is recorded on a photosensitive material corresponding to each of the image data by carrying out main scan of a plurality of light beams synchronously with moving the plurality of light beams relatively to a sub-scan direction of the photosensitive material, the method comprising the steps of: setting, based on a distance from a predetermined reference position on each photosensitive material to a position at which first main scan is started, the number of blank raster lines in the first main scan; and setting the blank raster lines from a leading end of the photosensitive material in a direction in which the photosensitive material is conveyed.
A fifteenth aspect of the present invention is an image recording method according to the fourteenth aspect, wherein the number of blank raster lines in the first main scan is set for each of the photosensitive materials so that a position at which main scan is started, which position including first image data, with respect to the predetermined reference position is substantially registered on each of the photosensitive materials.
A sixteenth aspect of the present invention is an image recording method using a multi-beam, in which one image data is separated into at least two colors, and based on the image data separated into at least two colors, an image is recorded by image recording means carrying out main scan of a plurality of light beams for an image while moving light beams relatively to a sub-scan direction of each of photosensitive materials. In this method, based on an amount of displacement of the photosensitive material in the sub-scan direction between a predetermined reference position and a position of a line at which main scan is started, blank raster lines of non-image data are set sequentially from the top of the plurality of light beams during the first main scan.
A seventeenth aspect of the present invention is an image recording method using a multi-beam, in which an image is recorded by dividing one image data into at least two colors and by carrying out main scan of a plurality of light beams for an image by image recording means while moving light beams relatively to a sub-scan direction of each of photosensitive materials. This method comprises the steps of: obtaining an amount of displacement in the sub-scan direction of each of photosensitive materials corresponding to the same image from a predetermined reference position to a position of a line at which main scan is started; setting the number of blank raster lines sequentially from a leading end of the photosensitive material in the sub-scan direction during main scan for other photosensitive materials so that the amount of displacement of a photosensitive material located at the position of a line at which main scan is started, with the amount of displacement being made largest, is limited to a pitch of one line at the maximum; and setting the top of lines not including the blank raster lines as an apparent position of a line at which main scan is started.
An eighteenth aspect of the present invention is an image recording apparatus using a multi-beam, in which based on image data obtained by separating one image into colors of cyan (C), magenta (M), yellow (Y), and black (BK), an image is recorded by carrying out main scan of N (N is an integer of 2 or more) light beams by image recording means while moving light beams relatively to a sub-scan direction of a photosensitive material. This apparatus comprises: photosensitive-material detecting means which is provided on a conveying path (a conveying path of the photosensitive material or a conveying path of light beams) along which light beams are moved relatively to the sub-scan direction of the photosensitive material and which detects a relative position of a line at which main scan is started between the photosensitive material and the light beams; main-scan-starting-position detecting means for detecting a position where recording of an image is started in the main scan; start-of-main-scan controlling means which controls the image recording means so as to start main scan after the photosensitive material and the light beams have reached the relative position of a line at which main scan is started by a signal from the photosensitive-material detecting means and when a signal from the main-scan-starting-position detecting means; calculation means which calculates an amount L of relative displacement between the photosensitive material and the light beams until the main scan is started from the relative position of a line at which main scan is started between the photosensitive material and the light beams; and blank raster line setting means which sets, based on a ratio R (0  less than R less than 1) of the amount of movement L calculated by the calculation means to a previously known amount of movement W in one sub-scan, blank raster lines sequentially from a leading end of the photosensitive material in the sub-scan direction, which blank raster lines increases as the ratio R becomes smaller with the upper limit of the number of blank raster lines, Nxe2x88x921, being smaller than the number N of light beams by one in the first main scan by the image recording means.
According to the first aspect of the present invention, when one image is formed by superposing separated images recorded on the respective photosensitive materials one another, it is necessary that relative positions of the separated images on the respective photosensitive materials be provided to coincide with one another so that the separated images can be properly superposed on one another.
When the images are recorded by repeatedly carrying out main scan while the photosensitive materials are being subjected to sub-scan, there are cases in which positions at which writing (recording) of the each of the separated images is started on the respective photosensitive materials may be different. Namely, a distance between a predetermined reference position on the photosensitive material (for example, a position of the leading end of the photosensitive material) and a position at which the first main scan is started varies for each of the photosensitive materials. Therefore, as the number of light beams (the beam number of multi-beam) in one main scan increases, the above-described distance (in the direction in which the photosensitive material is conveyed) may become longer.
For this reason in the first main scan, blank raster lines of non-image data are set. Namely, by setting a non-recording region (line) on the photosensitive material, an actual position at which recording of an image is started can be displaced backward in the direction in which the photosensitive material is conveyed, and the positions at which recording of the images are started on the photosensitive materials can be made coincident with one another.
An optical system used for the main scan, for example, a polygon mirror or a resonant mirror, is provided to mechanically swing (rotate) a surface by which a light beam is reflected so as to distribute the light beam on the photosensitive material in a main scan direction. For this reason, when the photosensitive material is conveyed to a position in which recording of an image can be started immediately after the optical system is brought into an initial state (that is, a state in which main scan for the photosensitive material can be started), recording of the image is cannot be carried out until the optical system is brought into the initial state again. On the other hand, when the optical system is brought into the initial state synchronously with (or immediately after) the photosensitive material having been conveyed to the position at which recording of an image can be started, recording of the image can be started immediately.
As described above, when the time at which the main scan is started varies greatly, the relative positions of the separated images on the respective photosensitive materials do not coincide with one another due to sub-scan for the photosensitive material is being continuously carried out.
Accordingly, as described in the second and fifth aspects of the present invention, the number of blank raster lines in the first main scan is set for each section of the photosensitive material, based on a distance between a predetermined reference position on each section of the photosensitive material and a position at which the first main scan is started on that section, also, the blank raster lines are set in order from a leading end of the sheet of photosensitive material, the blank lines being substantially transverse to a direction in which the sheet of photosensitive material is conveyed.
For this reason, based on the distance in the direction in which the photosensitive material is conveyed, in the first main scan, blank raster lines of non-image data are set sequentially from the leading end of the photosensitive material in the direction in which the photosensitive material is conveyed. Namely, by setting a non-recording region (line) on the photosensitive material, an actual position at which recording of an image is started can be displaced, based on the distance in the conveying direction, backward in the direction in which the photosensitive material is conveyed, and the positions at which recording of the images are started on the photosensitive materials can be made coincident with one another.
As a result, the relative positions of the separated images on the respective photosensitive materials can be made coincident with one another.
A sixth aspect of the present invention is an image recording apparatus in which an image is recorded by applying a plurality of light beams (for example, N light beams) on photosensitive materials for each of the colors C, M, Y, and K which are required for forming a so-called full-color image or the like. According to the sixth aspect of the present invention, the state in which the photosensitive material is conveyed to the position at which recording of an image can be started is detected by the photosensitive-material detecting means (sensor), and subsequently, the state in which main scan by the plurality of light beams can be started is detected by a means (sensor) for detecting the state in which a main scan can be started.
When the state in which main scan by the plurality of light beams can be started is detected by the sensor for detecting the state in which a main scan can be started after the state in which the photosensitive material is conveyed to the position at which an image can be recorded is detected by the photosensitive-material detecting sensor, namely, after a predetermined signal is outputted from the photosensitive-material detecting sensor and when a predetermined signal is outputted from the sensor for detecting the state in which a main scan can be started, the sensor for controlling start of main scan which is provided to control the image recording means (section) starts main scan. At this time, the position at which recording of an image is started on each photosensitive material may be displaced in the sub-scan direction by an amount W of movement for one sub-scan at the maximum. The amount W of movement for one sub-scan corresponds to an amount by which the photosensitive material is conveyed in one main scan, and as the number of light beams increases, the amount W of movement becomes larger.
A calculation means (data processor) calculates an amount L by which the photosensitive material is conveyed during a time between a time at which the state in which the photosensitive material is conveyed to the position in which an image can be recorded is detected by the photosensitive-material detecting sensor, and a time at which the state in which main scan by the plurality of light beams can be started is detected by the sensor for detecting the state in which main scan can be started. The ratio R (0  less than R less than 1) of the amount L by which the photosensitive material is conveyed with respect to the amount W of movement for one sub-scan is obtained.
In the first main scan as in the seventh to tenth aspects of the present invention, blank raster lines whose number increases as the ratio R becomes smaller are set, based on the above-described ratio R, sequentially from the leading end of the photosensitive material in the direction in which the photosensitive material is conveyed. The upper limit of the number of blank raster lines is smaller than the number N of light beams by one.
Accordingly, in the case of xe2x80x9cthe most suitable timingxe2x80x9d, the first main scan lines, Nxe2x88x921, are blank raster lines, and the position at which recording of an image is started in the case of xe2x80x9cthe most unsuitable timingxe2x80x9d is displaced only by a pitch of one line at the maximum. As a result, an image of high quality in which no color displacement occurs can be obtained.
According to the sixteenth aspect of the present invention, when one image is formed by superposing images recorded on the photosensitive materials one another, it is important that these images be registered. Further, it is necessary that relative positions of images and photosensitive materials be provided to coincide with one another.
When an image is recorded by carrying out main scan repeatedly while moving the light beams relative to the sub-scan direction of the photosensitive material, a position at which writing is started may vary between photosensitive materials. Namely, the time that the relative position between the photosensitive material and the light beams reaches from a predetermined reference position on the photosensitive material (for example, a leading end of the photosensitive material) to the position of a line at which main scan is started has no correlation with one another, and therefore, as the number of multi-beams increases, an amount of displacement in the sub-scan direction becomes larger.
For this reason, based on the amount of displacement of the photosensitive material in the sub-scan direction, blank raster lines of non-image data are set sequentially from the top of the plurality of light beams during the first main scan. Namely, by providing lines apparently having nothing recorded therein, a leading end of an image is displaced backward in the sub-scan direction of the photosensitive material by a region of the blank raster lines so as to correspond to a photosensitive material displaced by the largest amount.
According to the seventeenth aspect of the present invention, an amount of displacement of the photosensitive material in the sub-scan direction from a predetermined reference position (for example, the leading end of the photosensitive material) to the position of a line at which main scan is started is obtained.
An optical system used for the main scan, for example, a polygon mirror or a resonant mirror, is provided to mechanically swing (rotate) a surface by which a light beam is reflected so as to distribute the light beam on the photosensitive material in a main scan direction. For this reason, when the photosensitive material and the light beam reach the relative position of a line at which main scan is started immediately after the optical system passes an initial position, recording of the image cannot be carried out until the optical system is brought into the initial state again. On the other hand, when the optical system is brought into the initial state immediately after the photosensitive material and the light beam has reached the relative position of a line at which main scan is started, recording of the image can be started immediately.
As described above, when the time at which the main scan is started varies greatly, the relative positions of images on the photosensitive materials do not coincide with one another due to sub-scan for the photosensitive material being continuously carried out.
The number of blank raster lines are set sequentially from a leading end in the sub-scan direction of a photosensitive material at a position of a line at which main scan is started, which the position is displaced by the largest amount, in the main scan for other photosensitive materials, and the top of lines not including the blank raster lines is set as an apparent line at which recording of an image is started. As a result, the photosensitive material displaced by the largest amount is limited to an amount of displacement of pitch of one line at the maximum, and therefore, the amount of displacement can be regarded as that in an allowable range.
The eighteenth aspect of the present invention is an apparatus for recording an image by applying a multi-beam (N light beams) to four sheets of photosensitive material for colors of C, M, Y, and BK which are required for forming a so-called full-color image. According to this aspect, the position of a line at which main scan is started is detected by the photosensitive-material detecting means, and subsequently, the position at which recording of an image is started is detected by the start-of-main-scan detecting means.
The calculation means calculates the amount of relative movement L between the photosensitive material and the light beam until the main scan is started from the relative position of a line at which main scan is started between the photosensitive material and the light beam, and the ratio R (0  less than R less than 1) of the amount of movement L to the amount of movement W in one sub-scan is obtained.
Blank raster lines whose number increases as the ratio R becomes smaller are set, based on the above-described ratio R, sequentially from the leading end of the photosensitive material in the direction in which the photosensitive material is conveyed (blank raster line setting means). The upper limit of the number of blank raster lines is smaller than the number N of light beams by one.
Accordingly, in the case of xe2x80x9cthe most suitable timingxe2x80x9d, the first main scan lines, Nxe2x88x921, are blank raster lines, and the position at which recording of an image is started in the case of xe2x80x9cthe most unsuitable timingxe2x80x9d is displaced only by a pitch of one line at the maximum. As a result, an image of high quality in which no color displacement occurs can be obtained.